There is the transient diffraction grating method as one of methods used to measure information upon diffusion of particles. For example, Patent Document 1 discloses a method to measure a diffusion constant by means of the transient diffraction grating method, thereby detecting protein association based upon a change of the diffusion constant.
According to the conventional transient diffraction grating method, two pulse excitation light beams with the same wavelength are irradiated upon a sample such that the beams cross each other, thereby forming interference fringes within the sample. While molecules (particles) in the sample present in bright portions of the interference fringes formed by the pulse excitation light beams are photoexcited, molecules (particles) in the sample present in dark portions of the interference fringes are not photoexcited, the photoexcited molecules and non-photoexcited molecules are alternately present in a regular arrangement in an area where the interference fringes are formed. If the diffusion coefficient of excited state is different from non-excited, and diffraction grating (transient diffraction grating) is temporarily generated in their diffusion process.
Also, in case molecules that have photochemical reactivity with target molecules are mixed with, reaction occur in bright portions in the fringe. Reacted molecules should have smaller diffusion coefficient, transition grating is generate in their diffusion process.
When a probe light beam is additionally irradiated upon the area where the transient diffraction gratins are formed, the probe light beam is diffracted by the transient diffraction grating. After the photo excitation process is occurred, the molecules that has smaller diffusion coefficient are diffuse more rapidly than molecules in another state. The transient diffraction grating is formed in the first diffusion process, and is extinguished in the second diffusion process, which is caused by the molecules that has larger diffusion coefficient, grating and an intensity of diffracted light beams generated from the probe light beam by the transient diffraction grating appear and vanish. On this occasion, a decay curve or raising curve of the intensity of the diffracted light beam represents two diffusion constants (diffusion coefficients) of the molecules with each state in the sample, and it is thus possible to calculate the diffusion coefficients of the molecules in the sample based upon the obtained curves, and to further obtain information on a size (particle diameter), a shape, and interaction with a solvent of the particles in the sample based upon the diffusion coefficient.
Moreover, as a method used to measure information upon a diffusion of particles, the inventors of the present invention propose such a device and a method that an electrode pair in a comb shape configured by electrically connecting one ends of multiple electrode teeth is arranged in a container storing a sample having particles dispersed in a medium such that the other ends of the electrode teeth of the respective electrodes are opposed to each other at a minute interval, a voltage is impressed upon the electrode pair to generate a regularly arranged electric field between the electrode teeth opposing to each other, a phoretic force thus acts upon the particles in the sample in the container to generate diffraction grating formed by a density modulation of the particles, after the generation of the diffraction grating, the impression of the voltage upon the electrode pair is stopped to diffuse the particles thereby extinguishing the diffraction grating, there is simultaneously detected an intensity of a diffracted light beam obtained by irradiating a light beam upon a portion where the diffraction grating are generated in the container, and information on the diffusion of the particles in the sample is evaluated based upon a temporal change of the intensity of the diffracted light beam in the extinction process of the diffraction grating.
[Patent Document] Japanese Patent Laid-Open Publication No. 2004-85528